Apparatus for irradiating body tissue with laser light

ABSTRACT

In an apparatus used to irradiate body tissue with high-intensity laser light, a probe with at least one waveguide is used which can be coupled with a laser light source and which at its light-exiting section, which can be inserted in the body tissue, is equipped with a diffuser element which consists of a base material that is highly transparent to the laser light and, dispersed therein, scattering particles that deflect the light rays, and with a first cover tube that surrounds the waveguide at a distance, that connects to a coolant source, that is open at its distal end and that, at least in the region of the diffuser element, is made of a transparent and good heat-conducting material, a device for modifying beam intensity is situated in the path of the laser beam before the input coupling point, with the waveguide in the region of the light-exiting section being surrounded by a reflector and/or absorber that has at least one light outlet in the region of the target radiation surface.

The invention relates to a device for irradiating body tissue with highintensity light, the device including a probe with at least onewaveguide couplable with a laser light source on whose light exitsection (which is insertable into body tissue) a diffuser element isprovided which consists of a base material highly transparent for thelaser light and scattering particles dispersed in this which deflect thelight rays, and with a first cover tube surrounding the waveguide at adistance which can be connected with a coolant source, which is open atits distal end, and which consists of a transparent and good heatconducting material.

BACKGROUND OF THE INVENTION

The laser has been used since 1983 for interstitial heating ofbiological tissue. In the meantime, various probes and applicators havebeen developed to irradiate laser light into human tissue. Correspondingdevices are described in German patent applications open to publicinspection 38 13 227, 41 37 983, 42 13 053 and 42 21 364.

The previously described systems are constructed according to one moreor less similar principle. The laser light is launched into an opticalelement located in the tip of the waveguide through a waveguide. Here asa rule it is a question of mirrors or prisms as well as specialdiffusers which permit an even irradiation of the laser light in alldirections of space. These systems are provided in part with a coolingcircuit for an additional modification of the temperature area profile,as this is, for example, described in DE-A-42 21 364, from which thepreamble of claim 1 proceeds. A main problem of all interstitial heatingprocedures is, however, the exact adaptation of the temperature areaprofiles to the given tissue lesion. This will be sketched briefly withreference to the example of prostatic hyperplasia.

The prostate is divided anatomically into a right and a left prostatelobe as well as a median lobe. The geometrical extension is indeedsimilar in a normal prostate, apart from differences in size. Theintensities of pathological changes are, however, extraordinarilydifferent from patient to patient. In addition to a general enlargementof the prostate, there are also found isolated changes in the right orleft prostate lobes as well as in the median lobe. Moreover, of course,very different combinations of these pathological changes can occur inindividual cases. In addition to this, it frequently results that thetarget tissue reacts differently to laser radiation although theirradiation profile was adapted to the lesion. The temperaturedistribution can thus assume undesirably excessively high or, however,even too low temperatures during the irradiation. A similar problememerges in connection with irregularly formed tumors, whereby especiallythe histological composition within the tumor (living cells, necroses,hemorrhages, vessels) can supervene in an aggravating manner. A laserprobe which solves this problem has not been described until now.

SUMMARY OF THE INVENTION

A probe for irradiating body tissues with laser light is known fromEP-A-439 629, which for achieving a uniform irradiation has a diffuserelement and in which a reflector with light exit openings so surroundsthe waveguide in the region of its light exit section that lightpreferably is emitted in the forward direction.

Underlying the invention is the object of constructing a device of thetype named at the beginning such that it can be used in connection witha great number of specific pathological anatomical lesion shapes andpermits an online adaptation of the laser output to various reactionswithin the irradiated tissue during the irradiation process.

This object is accomplished by arranging an installation in the path ofthe laser beam before the launching point for changing the beamintensity, and the waveguide is enclosed by a reflector and/or absorberin the area of its light exit section which has at least one light exitopening in the area of the desired radiation surface.

A first basic feature of a preferred embodiment of the solution of theinvention concerns the launching of the laser light into the probe aswell as the waveguide within the same. In contrast with known systems,the laser beam is split into the required number of component beams bymeans of a beam-splitting arrangement. Alternatively to or supplementalto this, the laser light source can have a multiplicity of individuallasers. Only then is the laser light launched into the probe whichincludes several waveguides. In accordance with a further essentialfeature, a facility for changing the radiation intensity is insertedbetween the beam-splitting arrangement and the probe per component beamwhich can be regulated continuously with, for example, the aid of astepper motor.

The individual waveguides end on the tissue side, that is, on the distalend of the probe in a diffuser element which consists of a base materialin an inherently familiar manner which is highly transparent for thelaser light used. A defined number of scattering particles is introducedinto this material. As an essential feature, however, the individualdiffusers are encapsulated in accordance with the invention with ahighly reflective material, whereby the reflector so constructed has anopening solely in the area of desired irradiation. Here it must inparticular be pointed out that a redirection of the beam with the aid ofa prism or mirror in the light exiting area does not suffice for aneffective irradiation. The beam must rather be as homogeneouslydistributed as possible over the entire exit area, as the high powerdensities otherwise occurring lead to an overheating of the tissue nearthe probe. On the other hand, however, a diffuser (even withasymmetrical distribution of the scattering particles, as described, forexample, in DE-OS 42 21 364) without reflecting jacketing is notsufficiently suited to prevent light exiting in an undesired directioncompletely. With the solution of the invention, the reflector enclosingthe diffuser ensures that light from the respective waveguide is onlyradiated in the desired direction. In this way, the direction andintensity of the radiated laser light can be selected in accordance withthe respective shape of the tissue to be irradiated. The number ofradiation elements is chosen corresponding to the application inquestion.

The measures for modifying the initial photon distribution in the tissueare nevertheless taken by themselves unsuited for solving the problem,as a symmetrical lesion arises again owing to temperature conduction inthe tissue despite asymmetrical irradiation. Only cooling the tissuenear the probe through the probe guarantees the asymmetrical lesion, asthrough this the temperature gradient created by light absorptionremains preserved in the tissue, and a temperature equilibrium betweenirradiated and not irradiated tissue areas is prevented. In addition,the cooling circuit serves for additional modification of thetemperature area profile.

The online regulation of the laser-tissue interaction requires anadequate temperature monitoring. According to the construction of thedevice, the probe is therefore additionally provided with at least atemperature sensor, for example a thermocouple.

Spot temperature measurements are as a rule insufficient, withasymmetrical temperature area profiles. This holds especially forindications in connection with which, owing to tissue inhomogeneity,varying temperature courses are to be expected. Here a three dimensionaltemperature monitoring is necessary for an indicative temperaturemeasurement. Monitoring the irradiation process with the aid of nuclearspin tomography represents a practicable solution. The whole bodyspooling used at this time, however, is limited with respect to itsresolution of detail, for example the urethral wall.

In accordance with a preferred embodiment of the invention, the probe,therefore, includes an additional antenna for direct local applicationof the high frequency radiation necessary for diagnosis by means ofusual nuclear spin tomography. In addition, the antenna can also beconnected as a receiving antenna, or an additional receiving antenna canbe provided to receive the high frequency radiation emitted by thenuclear spin tomograph. This antenna can also be used for application oftherapeutic radiation doses.

Other advantageous configurations of the invention are indicated in theclaims.

BRIEF DESCRIPTION OF THE INVENTION

Further features and advantages of the invention emerge from thefollowing description which explains the invention on the basis ofembodiments in connection with the appended drawings. Depicted are:

FIG. 1 A schematic representation of the part of the device connectedwith the proximal end of the probe with a laser light source, abeam-splitting arrangement and a heat exchange installation,

FIG. 2 A schematic section containing the axis through the distal endregion of the probe,

FIGS. 3 to 6 Schematic cross sections through the probe along the lineIII--III in FIG. 2, whereby the outer cover tube of the probe is notrepresented,

FIG. 7 A section representation corresponding to FIG. 2 through a probein accordance with a second embodiment of the invention,

FIG. 8 A section corresponding to FIGS. 3 to 6 through the secondembodiment of the probe along line VIII--VIII in FIG. 7,

FIG. 9 A schematic representation of the practical use of the probe inirradiation of the prostate, and

FIG. 10 A section along line X--X in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a laser 10, the initial beam of which is launchedinto a beam-splitting arrangement 14 by means of an optical system 12.The beam-splitting arrangement here includes, for example, two beamsplitters 16, 18 arranged one behind the other and two mirrors 20, 22which break down the launched beam of the laser 10 into three componentbeams in the manner represented. The number of beam splitters must, ofcourse, be varied according to the desired number of component beams.The component beams are at all times launched into one waveguide 26 eachthrough an optical system 24. Between the exit of the beam-splittingarrangement 14 and the respective optical system 24, a facility forchanging the intensity of the component beam is arranged in eachcomponent beam, for example, a variable filter 28. The attenuation ofthe beam can alternatively also take place with rotating mirror prismsor glass plates. The variable filter can, for example, be continuouslyregulated with the help of a stepper motor.

The device represented in FIG. 1 furthermore includes a cooling circuitto cool the probe with an inflow 32, an outflow 34 and a pump/heatexchange unit 36 for pumping and tempering the coolant.

The probe proper is connected to the device schematically represented inFIG. 1, the distal end section of which is represented in FIG. 2. Anoptical fiber bundle 38 consisting of the waveguides 26 which isappropriately enclosed by an additional casing 40 (for example, hose,tube) for better mechanical stability is located in the center of theprobe to be introduced into the tissue. The waveguides or glass fibers26 end distally in a radiating head which will be explained in greaterdetail on the basis of FIGS. 3 to 6. The fiber bundle 38 is enclosed ata radial distance by an inner first cover hose or cover tube 44, whichis open at its distal end, and which forms the inflow 32 for thecoolant. This inner cover tube is for its part enclosed at a radialdistance by a second cover tube 46 which is closed on its distal end,and which forms the outflow or return for the coolant. The end section48 of the inner cover tube which encloses the radiation head 42 and thecorresponding cap-like closed end section 50 of the outer cover tube 46are made of a material with good transparency for the laser radiationused in any given case. The material used for the transparent cup plug50 must above and beyond this be a good heat conductor.

The radiation head 42 will now be explained in greater detail on thebasis of FIGS. 3 to 6.

With the embodiment in connection with FIG. 3, each wave guide 26 endsin a diffuser 52. A combination of a highly transparent base material(methyl methacrylate or similar materials, glass or glass-likematerials) and dispersed scattering centers (for example, bariumsulfate, magnesium oxide and similar scattering substances, air bubblesor foam glass) is used as material for the diffuser. The diffuser is atall times partially enclosed by a highly reflective casing 54. Thediffuser so encapsulated only has an opening 56 in the desiredirradiation area. Any highly reflecting material (for example, gold,aluminum and the like) for the wavelength used comes into considerationfor the capsule material.

With the embodiment represented in FIG. 4, the three partiallyencapsulated diffusers are dispersed as a whole in a diffuser 58. Ifneed be, the inner diffusers 52 can be omitted with this solution.

With the embodiment represented in FIG. 5, the reflectors surroundingthe individual diffusers 52 are enclosed by a single cylindrical elementof a highly reflecting material which accommodates the waveguide endsections and the diffusers 52, and which again has correspondingopenings 56 in the radiation area. Even this element 60 can be embeddedin an external diffuser 62 as with the embodiment in accordance withFIG. 4, as FIG. 6 shows this. This permits a further modification of thetemperature area profile to be attained with the probe.

The respective inner diffusers 52 and outer diffusers 58, 62 can bemodified with respect to their scattering characteristics either bychanging the scattering particles in the base material or, however, by achange in the form of the diffuser. A change in the form of the internaldiffuser of course also requires a change in the form of the highlyreflective casing or reflector.

As one recognizes, the scattered light is only emitted in certaindirections owing to the reflectors 54, 60 provided in accordance withthe invention partially enclosing the ends of the waveguides 26. Inconnection with a control of the intensity of the launched light throughthe filter element 28, the intensity and direction of the radiated laserlight can consequently be controlled, and the radiation profiletherewith be adapted to the lesion of the irradiated tissue.

The circulating coolant permits a modification of the temperature areaprofile obtained by means of the irradiated energy. Monitoring thetemperature area profile can take place through temperature measurementsby means of one (temperature sensor 66 in FIG. 10) or severaltemperature probes, preferably with a nuclear spin tomograph. For thispurpose, an antenna 64 is provided with the embodiment in accordancewith FIG. 7 inside the inner cover tube 44 of the probe which makespossible a local irradiation of high frequency energy or a reception ofthe corresponding signals for nuclear spin tomographic monitoring. Theantenna can also be used for simultaneous irradiation of therapeuticradiation doses of high frequency energy of suitable wave length (forexample, 2.45 GHz), which permits an additional modification of thetemperature area profile. The diffuser element is moreover constructedas with the embodiment in accordance with FIG. 3.

The cooling circuit can be variously constructed in modification of theembodiments represented in FIGS. 2 and 7. In accordance with a firstvariant, only a cover tube with transparent end cap is used, whereby theinterstitial space between the optical fiber bundle 38 and the covertube is separated by a horizontal membrane such that the upper part ofthe tube is constructed as an inflow and the lower part of the tube asoutflow. With another variant, a liquid wave guide is used. By suitableselection of the liquid and waveguide, the inflowing liquid is directlyused as waveguide. The radiating element must in this case beconstructed porously if need be.

The probe can be variously constructed for adaptation to the anatomicalparticularities of its respective area of use. Thus, when using theprobe in connection with the prostate, the radiating unit will not liein the tip area as is the case with the embodiments in accordance withFIGS. 2 and 7. In accordance with FIG. 9, the radiating head 42 ispositioned such that it lies within the prostate 69. The tip of theprobe, however, can be advanced into the bladder 68. With such anembodiment, additional positioning aids are required if worse comes toworse, for example a balloon 70. This could be positioned either in theurinary bladder or, however, in the urethra itself. In connection withone construction variant, this balloon could also replace the outercasing of the probe. The outflow of the coolant would in this case takeplace between the inner cover tube and the positioning balloon, wherebythis must then again have good transparency and be an adequate heatconductor for the laser light used.

With a further, not represented embodiment, one can also completelymanage without the second casing in the area of the urethra when using asuitable positioning balloon. In this case, the urethra itself is usedas outflow. This offers the advantage that the coolant directly coolsthe urethra. In this case, a further balloon is positioned furtherdistally below the prostate in order to assure the irradiation shape.This has at its disposal a tube system in order to make the outflow ofthe coolant possible.

I claim:
 1. Device for irradiating body tissues with laser light of highintensity, said device comprising a probe with a plurality of waveguides(26) each couplable with a respectively associated one of a plurality oflaser beams from a laser light source (10), each of said waveguideshaving a light exit section insertable into body tissue provided with adiffuser element (52) which diffuser element consists of a base materialhighly transparent for the laser light and scattering particlesdispersed in said base material which particles deflect the light rays,and a first cover tube (44) surrounding the waveguides (26) at adistance so that said first cover tube can be connected with a coolantsource (36), said first cover tube having an open ended distal endportion surrounding said light exit sections of said waveguides and madeof a transparent and heat conducting material, there being arranged inthe path of each of said laser beams, in advance of the beam reachingits associated one of said waveguides, an installation (28, 30) forchanging the intensity of the beam, and each waveguide (26) beingenclosed at its light exit section by an element, selected from theclass consisting of a reflector (54) and an absorber, which element hasat least one light exit opening (56).
 2. Device according to claim 1,wherein between the laser light source (10) and the waveguides (26) abeam-splitting device (14) is positioned for splitting the beam of thelaser light source (10) into component beams.
 3. Device according toclaim 2, wherein the laser light source includes a number of individuallasers.
 4. Device according to claim 2, wherein the beam-splittingarrangement (14) with more than two waveguides (26) includes a number ofsuccessive beam-splitting elements (16, 18).
 5. Device according toclaim 1, wherein the installation for changing the intensity of eachbeam for each one of said beams includes an arrangement for reflectingthat one beam.
 6. Device according to claim 1, wherein the installation(28, 30) for changing the irradiation intensity includes an absorptionelement (28).
 7. Device according to claim 6, wherein the absorptionelement (28) is an optic light filter.
 8. Device according to claim 1,wherein the light exit section of each waveguide (26) is embedded in itsown diffuser element (52) which is enclosed by the reflector (54). 9.Device according to claim 1, wherein the element is jointly embedded inan external diffuser (58).
 10. Device according to claim 1, wherein thereflectors (54) enclosing the light exit sections of the waveguides (26)are embedded in an external diffuser (58).
 11. Device according to claim1, wherein the reflectors are the partial cylindrical walls of boringswhich are constructed in a reflector element (60).
 12. Device accordingto claim 1, wherein the base material for the diffuser (52, 58, 62) ischosen from the materials group comprising methyl methacrylate, glassand flexible transparent substances, and wherein the material for thescattering particles is selected from the materials group includingbarium sulfate, magnesium oxide and aluminum oxide.
 13. Device accordingto claim 1, wherein the scattering particles in the diffusers consist ofglass with a refraction index different from the base material or withglass inclusions.
 14. Device according to claim 1, wherein the firstcover tube (44) is surrounded at a distance by a second cover tube (46)to form an annulus between the two cover tubes (44, 46); said secondcover tube being closed off in the light exit sections of the waveguidesby a transparent cap (50) which conducts heat so that the first covertube (44) can be connected to a coolant supply (32) and the annulusbetween the two cover tubes (44, 46) can be connected to a coolantoutflow (34).
 15. Device according to claim 1, wherein the waveguides(26) are constructed as liquid waveguides and connected to a coolantinflow from the coolant source.
 16. Device according to claim 1, whereinthe probe is provided with a positioning aid in the form of at least oneballoon (70).
 17. Device according to claim 16, wherein the positioningaid is situated adjacent said light exit sections and is transparent anda heat conductor.
 18. Device according to claim 17, wherein thepositioning aid (70) is arranged outside the light exit sections of saidwaveguides.
 19. Device according to claim 1, having a rigid outer probecasing (46).
 20. Device according to claim 1, having a flexible outerprobe casing (46).
 21. Device according to claim 1, wherein the probehas at least one temperature sensor.
 22. Device according to claim 1,wherein the probe is manufactured of nuclear spin-compatible materials.23. Device according to claim 1, wherein the probe is constructed in theform of a catheter having a distal end provided with a tip for insertioninto solid tissue.
 24. Device according to claim 1, wherein the probehas at least one antenna for the irradiation and/or receiving of highfrequency energy.